Method of impregnating wood with chemical solutions



Patented Sept. 11, 1951 METHOD or mrasuna'rmc woon wrru chemical. sow'rrous.

Carl Brynoil Lundstrom, Little Falls, N. Y. Application January SI, 1947, Serial No. 724,107 2 Claims. (Cl. 144-309) 1his invention relates to methods for locally impregnating wood with chemicals preparatory densincation is localized it is practicable to use a greater degree of densiiicaticn than is desirable when the entire piece is densiiled.

In a prior application, Serial No. 831.432. died April 17. 1944. and issued as Patent 2,488,301. on November iii, 1949, I describe and claim a method for locally densifying wooden furniture components. This method requires. when resin form- ,in: chemicals are used, a deiinitely localised impresneticn with chemicals.

The present invention oiiers an inexpensive and commercially desirable method of securing localised impregnation, and gives the best results so far economically secured. It can be used when localization of impregnation is not necessary. but since an additional problem is present when localization is sought the invention will be described as so used.

The invention will now be described as used to impregnate a corner and portions of two adjacent faces of a desk leg blank which is square in cross section.

In the drawings:

Fig. l is a cross-section of a steam tray with blanks in place.

Fig. 2 is a cross-section of a tank containing an impregnating solution, and showing the blanks in place in a rack which allows several blanks to be handled as a unit. and insures the desired depth of immersion.

Figs. 3 and 4 are diagrammatic cross-sections of an elongated blank such as a desk leg after impregnation and showing how the blank is 10- cally densiiled by compressing it in suitably formed heated dies.

Fig. 5 is a cross-section of the iinished desk leg showing by dotted lines the original crosssection, and by stippling the densiiied portions.

As shown in Fig. l a steaming-tray ll closed at ends, sides and bottom, has parallel longitudinal bars i1 covered with resilient sealing strips ll- These extend from end to end of the tray and are spaced to receive the elongated blanks B of rectangular cross-section, as shown. The strips l8 produce seals with two opposite longitudinal corners. Thus, two adjacent longitudinal faces X and Y are exposed in the steam space which is within the tray below the blanks, while the two other faces are wholly outside the steam space. The blanks are of such length that they extend from end to end of the tank.

Live steam, at a pressure of a few pounds gauge, is admitted to the steam space above mentioned and is freely vented therefrom at I9, I.

Since the steam is delivered at a pressure above atmospheric, it necessarily enters at a temperature above 212 F. As a consequence of the drop to atmospheric pressure the steam within the steam space is not merely dry, it is superheated. However, condensation upon the initially cool surfaces X and Y of the blanks first wets the blanks, and they remain wet until their surface temperature approximates 212 F. at which time re-evaporation and consequent drying will occur. This surface heating of the two faces x, Y of the blanks involves penetration of heat inward from the surfaces. The depth of such penetration depends on the temperature of the steam and the duration of exposure to the steam, each of which obviously can be controlled.

when the blanks have been properly surface heated, they are transferred to a rack having supporting side members Ii and a slotted platform it. The blanks are set in the slots with their steamed faces X and Y down. The rack "-42 is then placed in a tank I! containing to the level ill l a chemical solution at about room temperature.

A suitable solution can be prepared as follows:

216 parts of H20 8 parts of NaOH 52 parts of borax 384 parts of DMU (dimethylolurea) 340 parts of urea readily available. Other resin forming solutions are given in the Loughborough Patent 2,313,953. See also Forest Products Laboratory Bulletin R-1277.

The treatment in cold solution tank l3 affects the same areas as were treated in tank 8 and continues for fifteen or twenty minutes, after which the blanks are removed and allowed to dry in moderately heated air (say 200 F.)

Blanks B so treated are then pressed between the heated dies C, D as indicated in Figs. 3 and 4 with the treated surfaces X and Y against the forming die D. Fig. 3 shows the start and Fig. 4 the finish of the pressing operation. The temperature of the die D is 300 F. or thereabout.

In Figs. 4 and 5 densification is indicated by stippling E and in Fig. 5 the original contour of the two densified surfaces is shown in dotted lines F. Obviously the original cross-section of the blank must exceed the finished cross-section so that there will be material for densiflcation.

If localized impregnation is not required blanks can be immersed completely, first in steam, and then in cold solution.

The blanks heated in the first phase of treatment have a greatly augmented ability to take up the cold solution when brought into contact therewith.

Except for pressure-vacuum treatment, which requires expensive apparatus and expensive supervision, and is not adapted to localized treatment, the above method gives the best results so far attained. These results are only slightly inferior to those attainable by pressure-vacuum treatment, and are entirely acceptable for localized densification according to the procedure of my prior application above identified.

What is claimed is:

1. The method of locally densifylng the surface portion of a wooden article in a limited surface area and for a limited depth beneath said surface area which consists in preparing a blank which is over-size in said surface area to an extent corresponding to the contemplated densification steaming the surface of the blank in said area while inhibiting the action of steam on the remaining area of the surface of the blank; continuing said steaming until the blank is at a temperature of at least 212 F. for a depth correspondin to the desired depth of densiflcation; contacting said area with a cold impregnating solution until the portion of the blank so heated is impregnated with said solution; and thereafter subjecting said blank to heat and forming pressure applied to said area whereby the article attains its final form and dimensions by densification of the portions so impregnated.

2. The method defined in claim 1 in which the impregnating solution carries a thermo-setting resin in condition to set when subjected to heat and pressure.

CARL BRYNOLF LUNDSTROM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,923,726 Heghinian Aug. 22, 1933 2,235,822 Boarclman Mar. 25, 1941 2,313,953 Loughborough Mar. 16, 1943 2,398,649 Kvalnes Apr. 16, 1946 

1. THE METHOD OF LOCALLY DENSIFYING THE SURFACE PORTION OF A WOODEN ARTICLE IN A LIMITED SURFACE AREA AND FOR A LIMITED DEPTH BENEATH SAID SURFACE AREA WHICH CONSISTS IN PREPARING A BLANK WHICH IS OVER-SIZE IN SAID SURFACE AREA TO AN EXTENT CORRESPONDING TO THE CONTEMPLATED DENSIFICATION; STEAMING THE SURFACE OF TEH BLANK IN SAID AREA WHILE INHIBITING THE ACTION OF STEAM ON THE REMAINING AREA OF THE SURFACE OF THE BLANK; CONTINUING SAID STEAMING UNTIL THE BLANK IS AT A TEMPERATURE OF AT LEAST 212* F. FOR A DEPTH CORRESPONDING TO THE DESIRED DEPTH OF DENSIFICATION; CONTACTING SAID AREA WITH A COLD IMPREGNATING SOLUTION UNTIL THE PORTION OF THE BLANK SO HEATED IS IMPREGNATED WITH SAID SOLUTION: AND THEREAFTER SUBJECTING SAID BLANK TO HEAT AND FORMING PRESSURE APPLIED TO SAID AREA WHEREBY THE ARTICLE ATTAINS ITS FINAL FORM AND DIMENSIONS BY DENSIFICATION OF THE PORTIONS SO IMPREGNATED. 